Introduction
In this project the measurements are given in both metric (mm) and imperial (inches). The metric dimensions are written first followed by the imperial
dimensions in brackets.
This project is a very basic 1800mm (6ft) high fence gate. It is an easy weekend project which can be made in a few hours but should be spread over two days as the concrete for the posts has to harden before the gate can be fitted.
I used the following lumber for this project:
100mm x100m (4x4) treated wood for the posts and header,
150mm x 25mm (1x6) treated wood for the vertical gate boards
and
75mm x 50mm (2x3) treated wood for the gate rails (horizontal pieces) and brace.
However, please note that the rails and braces can be pretty much anything such as 100mm x 50mm or 100mm x 25mm (2x4 or 1x4).
The purpose of this gate was to create access through a pipe and mesh fence. Although the mesh fence was only 900mm (36") high,
I made the gate 1800mm (72") high in case I decided to increase the height of the fence at a later time.
This is how I made the basic fence gate.

Positioning.
First I determined where I wanted the gate and how wide it should be.
I decided on 900mm (3ft) for the gate width, which meant that the posts
should be spaced apart the width of the gate plus 10mm (3/8") inch clearance each side.
In other words, the gap between the two posts would be 920mm (36 3/4").
I marked the post holes accordingly and dug the holes.

The post holes.
I dug the post holes to a depth of 600mm (24"). The ground was firm.
I have a favorite set of digging tools that I always use
when digging holes. See fig.2.
My digging arsenal consists of:
1). One standard spade with a 200mm (8") straight edge blade.
2). One spade with a blade that tapers down to 100mm (4") wide. I keep this spade razor sharp and use it mainly for cutting through tree roots.
3). One spade that I cut-to-shape myself out of a larger shovel. It has a 125mm (5") hooked blade and I use it to scoop all the loose stuff out of the holes.
4). Last but not least, a big steel bar 38mm (1 1/2') thick, 1800mm (6ft) long and with a chisel point. I use it to break up the ground in the hole.

The concrete
I mixed a batch of concrete in a wheelbarrow and half filled the holes. I checked that the posts were in the right position
then I filled
up the holes and rechecked the posts for plumb.
I made the concrete mix stiff enough so that the posts would stay in an upright position without needing any props.
For information on how to mix concrete click here.

The header
The next day when the concrete had hardened I trimmed the top of the posts to the correct height ready for the header.
The purpose of a header is to hold the posts parallel so that they cannot move inwards and cause the gate to jam.
I made the header out of 100mm x 100mm (4x4) stock.
I first cut it to the correct length (overall measurement from the outside of one post to the outside of the other)
and made a rebate 100mm (4") in from each end of the header and 50mm (2") deep.
I did this by making multiple saw cuts across the rebate area and then finishing off with a sharp chisel.
See fig.4 and fig.5.
I then nailed the header to the top of the posts (fig.6).